This invention relates generally to manufactured intraocular lenses and more particularly to novel accommodating intraocular lenses for implantation in the eye specifically within the capsular bag, or in the ciliary sulcus, of the eye from which the natural lens matrix has been removed. The invention also relates to a novel method of utilizing the intraocular lenses in the eye to provide the patient with lens accommodation capability, responsive to normal accommodative ciliary muscle action.
The human eye has an anterior chamber between the cornea and the iris, and a posterior chamber behind the iris, which contains a natural crystalline lens. A vitreous chamber behind the lens contains vitreous humor. A retina is located to the rear of the vitreous chamber. The crystalline lens of a normal human eye is defined by a crystalline lens matrix, which is enclosed in a lens capsule. The lens capsule is attached about its periphery to the ciliary muscle of the eye by zonules. The lens capsule has elastic, optically clear, anterior and posterior membrane-like walls commonly referred by ophthalmologists as anterior and posterior capsules, respectively. Between the iris and ciliary muscle is an annular crevice-like space called the ciliary sulcus.
The human eye possesses natural accommodation capability. Accommodation refers to an optical function in which the lens can focus naturally, from a far distance, to a relatively near distance e.g. within a few centimeters of the eye. Natural accommodation involves relaxation and constriction of the ciliary muscle, as instructed by the brain, to provide the eye with near and distant vision. This ciliary muscle action is automatic, as instructed by the brain, and shapes the natural crystalline lens to the appropriate optical configuration for focusing, on the retina, the light rays entering the eye from the scene being viewed. It is well known that there is a relentless loss of this near focusing ability in middle age. Such condition can be treated with bi-focal or tri-focal glasses or contact lenses.
The human eye is also subject to a variety of other physiological disorders, which can degrade, or totally destroy, the ability of the eye to function properly. One of the more common of these disorders involves progressive clouding of the natural crystalline lens matrix resulting in the formation of what is commonly referred to as a cataract. It is now common practice to treat a cataract by surgically removing the cataractous human crystalline lens and, in a second step of the same surgical procedure, implanting an artificial intraocular lens in the eye to replace the natural lens.
Thus, if the natural lens becomes cloudy, as with a cataract condition, the natural lens is removed by an extraction procedure which leaves intact, within the eye, the posterior portion of the natural lens capsule, and at least a remnant of the anterior portion of the natural lens capsule. The removed natural lens is replaced with a manufactured intraocular lens. If the replacement lens is a mono-focal lens, the cloudiness may have been effectively treated, but the inability to adjust focal length will not have been treated, whereby glasses or contact lenses are still required for proper vision.
Monofocal lenses focus at one set focal length in front of the eye, for example either at far distance such as greater than 6 meters, or at a lesser distance nearer the eye. The human eye with its own natural lens can change shape, thereby to focus naturally at all such distances, but gradually loses this ability, to change shape, as the natural lens hardens with age. The ability of the natural lens, to change shape as so urged by the contraction of the ciliary muscle, thus to change focal length of the eye, whereby the eye can focus at any of a range of distances, is completely lost after cataract surgery when the manufactured replacement lens is a monofocal lens.
Newer designs of conventional manufactured intraocular lenses offer differing solutions to this problem of loss of accommodation. One such design is a lens which has a single posteriorly placed optic and hinged haptics, which enables the lens to translate forward with the pressure rise in the vitreous chamber, which pressure rise accompanies accommodation as signaled from the brain. The limitation of this design is that the maximum accommodation enabled by lens translation is typically only about 1.5 diopters for a 1 mm anterior translation of the lens. While a 1 mm translation is typical, modest differences in translation capability attend respective different eyes. Thus, actual diopter achievements depend both on the power of the intraocular lens, and the axial length of the eye.
Another relatively newer conventional manufactured intraocular lens design uses two lenses, which are hinged, or otherwise connected, together and implanted inside the natural lens capsular bag. The anterior manufactured lens has e.g. high plus power, while the posterior manufactured lens has a negative power. When the two lenses separate under accommodative tension, the anterior lens moves forward and the posterior lens moves backward, achieving a relatively higher calculated accommodation, which is less dependent on intraocular lens powers and/or axial lengths of the eye.
Yet another conventional intraocular lens design provides multiple lens elements or components in side-by-side relationship, in a single lens body, the respective side-by-side lens elements having different, but fixed, refractive powers.
Still another conventional intraocular lens design provides an intraocular lens which consists of a flexible transparent lens envelope filled with a transparent fluid. The envelope is attached to the ciliary muscle by means of a fastening fringe, which is in turn anchored to the lens envelope. The ciliary muscle acts as it does on the natural lens. Thus, when the ciliary muscle contracts, the lens becomes more spherical, and thus achieves a greater refractory power. When the ciliary muscle elongates, tension is exerted on the envelope, and flattens the envelope, reducing refracting power, which accommodates far vision.